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A feeding device includes: a sheet housing unit; a sheet conveying unit
having an endless belt member, which faces a topmost sheet of sheets
stacked in the sheet housing unit, and a suction unit disposed inside the
belt member; a sheet lifting unit that lifts the topmost sheet to a
position where the topmost sheet is attracted on a surface of the belt
member by a negative pressure generated by the suction unit; and an
external device sheet conveying unit that conveys a sheet fed from
another feeding device connected to the feeding device to a gap between
the topmost sheet in the sheet housing unit and the belt member. In
feeding the sheet fed from the other feeding device to the subsequent
step, the sheet lifting unit is stopped while the suction unit, the belt
member, and the external device sheet conveying unit are operated.

Inventors:

Fuda; Munehisa; (Miyagi, JP)

Assignee:

Ricoh Company, LimitedTokyoJP

Serial No.:

929467

Series Code:

12

Filed:

January 27, 2011

Current U.S. Class:

271/12

Class at Publication:

271/12

International Class:

B65H 5/08 20060101 B65H005/08; B65H 5/02 20060101 B65H005/02

Foreign Application Data

Date

Code

Application Number

Feb 4, 2010

JP

2010-023499

Claims

1. A feeding device comprising: a sheet housing unit in which a plurality
of sheets, nearly horizontal, is stacked; a sheet conveying unit that
includes an endless belt member, which faces a top surface of a topmost
sheet positioned at top of the sheets stacked in the sheet housing unit
and is disposed to have a gap from the top surface of the topmost sheet
when feeding of the sheets stacked in the sheet housing unit is not
performed, and a suction unit disposed inside the belt member, the sheet
conveying unit attracting the topmost sheet on an outer surface of the
belt member by generating a negative pressure in the suction unit and
conveying the attracted topmost sheet towards a subsequent step by
endlessly moving the belt member; and a sheet lifting unit that lifts the
topmost sheet to a position where the topmost sheet is attracted on the
surface of the belt member by the negative pressure generated by the
suction unit, wherein the feeding device is configured to be connected to
another feeding device that houses sheets and to feed the sheet fed from
the other feeding device to the subsequent step, the feeding device
further comprises an external device sheet conveying unit that conveys
the sheet fed from the other feeding device to the gap between the
topmost sheet in the sheet housing unit and the belt member, and in
feeding the sheet fed from the other feeding device to the subsequent
step, the sheet lifting unit is stopped while the suction unit, the belt
member, and the external device sheet conveying unit are operated.

2. The feeding device according to claim 1, wherein the sheet lifting
unit is an air discharging unit that lifts one end portions of the
topmost sheet and other sheets near the topmost sheet and separates a
plurality of sheets near the topmost sheet one from the other by blowing
air towards the one end portions of the sheets near the topmost sheet of
the sheets stacked in the sheet housing unit.

3. The feeding device according to claim 1, further comprising: a sheet
top position detecting unit that detects a height of the top surface of
the topmost sheet; a bottom plate that supports a bottom surface of the
sheets stacked in the sheet housing unit; an elevating unit that elevates
the bottom plate in a vertical direction; and an elevation control unit
that controls operation of the elevating unit based on a detection result
of the sheet top position detecting unit such that the height of the top
surface of the topmost sheet of the sheets on the bottom plate comes to a
given height, wherein the sheet top position detecting unit includes a
top surface contacting member that is brought into contact with the top
surface of the topmost sheet and changes its position in response to
changes in the height of the top surface, a top surface height detecting
sensor that detects the changes in the height of the top surface of the
topmost sheet by detecting the changes in the position of the top surface
contacting member, and a contacting member position control unit that
controls a position of the top surface contacting member regardless of
the height of the top surface of the topmost sheet, the top surface
height detecting sensor is disposed above an external sheet feed path
along which the sheet conveyed towards the gap between the topmost sheet
and the belt member by the external device sheet conveying unit passes,
and the contacting member position control unit controls the position of
the top surface contacting member so that a lower end of the top surface
contacting member comes above the external sheet feed path when the sheet
fed from the other feeding device is fed to the subsequent step.

4. An image forming apparatus comprising: an image forming section that
forms an image on a sheet of a recording medium; and a paper feeding unit
that feeds the sheet to the image forming section and comprises: a sheet
housing unit in which the plurality of sheets, nearly horizontal, is
stacked; a sheet conveying unit that includes an endless belt member,
which faces a top surface of a topmost sheet positioned at top of the
sheets stacked in the sheet housing unit and is disposed to have a gap
from the top surface of the topmost sheet when feeding of the sheets
stacked in the sheet housing unit is not performed, and a suction unit
disposed inside the belt member, the sheet conveying unit attracting the
topmost sheet on an outer surface of the belt member by generating a
negative pressure in the suction unit and conveying the attracted topmost
sheet towards a subsequent step by endlessly moving the belt member; and
a sheet lifting unit that lifts the topmost sheet to a position where the
topmost sheet is attracted on the surface of the belt member by the
negative pressure generated by the suction unit, wherein the feeding
device is configured to be connected to another feeding device that
houses sheets and to feed the sheet fed from the other feeding device to
the subsequent step, the feeding device further comprises an external
device sheet conveying unit that conveys the sheet fed from the other
feeding device to the gap between the topmost sheet in the sheet housing
unit and the belt member, and in feeding the sheet fed from the other
feeding device to the subsequent step, the sheet lifting unit is stopped
while the suction unit, the belt member, and the external device sheet
conveying unit are operated.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and incorporates by
reference the entire contents of Japanese Patent Application No.
2010-023499 filed in Japan on Feb. 4, 2010.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a feeding device provided to an
image forming apparatus such as a copying machine, a facsimile, and a
printer. Particularly, the present invention relates to a feeding device
that attracts a sheet at the top of sheets stacked in a sheet housing
unit onto a belt member and feeds the sheet to a subsequent step such as
an image forming section by the surface movement of the belt member, and
an image forming apparatus provided with the feeding device.

[0004] 2. Description of the Related Art

[0005] In a feeding device provided to an image forming apparatus and the
like, it is important to accurately send out one by one among a plurality
of sheets such as recording sheets stacked in a sheet housing unit and
thus, a separating mechanism that separates the stacked sheets one by one
is required. Generally, separating mechanisms employ a frictional
separation method by which a sheet sent from a sheet housing unit by a
pick-up roller is separated and fed by frictional force. Examples of the
frictional separation type separating mechanisms include a combination of
a separating roller and a friction pad and a combination of a separating
roller and a reverse roller.

[0006] As a feeding device provided with a separating mechanism different
from the frictional separation type, Japanese Patent Application
Laid-open No. 2007-45630 proposes a feeding device that separates and
feeds a sheet using a flow of air. The outline of the feeding device that
uses the flow of air to separate and feed a sheet will be explained
below.

[0007] A feeding device 200 illustrated in FIG. 16 is provided with a
paper feed tray 6 that is a sheet housing unit where a plurality of
sheets of paper P is stacked, which are nearly horizontal, and a suction
belt 2 arranged with a suction device 40 inside the suction belt. The
feeding device 200 is further provided with a blowing device 1 that blows
air as indicated by the arrow A in FIG. 16 towards the vicinity of the
leading edge in a conveying direction (arrow D direction in FIG. 16) of a
topmost paper P1 positioned at the top of the paper P placed in the paper
feed tray 6. Operating the suction device 40 generates a negative
pressure to cause the flow of air as indicated by the arrow B in FIG. 16
that acts to attract the paper P on the lower outer surface of the
suction belt 2.

[0008] In the feeding device 200, the blowing device 1 blows air to send
the air between the sheets of paper P to lift the topmost paper P1 up to
the height of the suction belt 2. The topmost paper P1 reached the height
of the suction belt 2 is attracted on the lower outer surface of the
suction belt 2 by the act of the negative pressure generated by the
suction device 40. Thereafter, by the surface movement of the suction
belt 2 as indicated by the arrow C in FIG. 16, the topmost paper P1
attracted on the suction belt 2 is conveyed towards the direction
indicated by the arrow D in FIG. 16 to reach an image forming section
that is a subsequent step and then, image forming is performed.

[0009] The blowing device 1 not only lifts the topmost paper P1 up to the
height where it is attracted on the suction belt 2, but also separates
the leading edge portion side of sheets of the paper P by sending the air
between the sheets of paper P. The topmost paper P1 of the paper P with
the leading edge portion being separated is attracted on the suction belt
2 and conveyed, thereby allowing the topmost paper P1 to be separated
from the other paper P and only the topmost paper P1 to be fed.

[0010] The feeding device 200 is also provided with a sheet top sensor 3
that detects the height of the top surface of the topmost paper P1 for
maintaining a distance h between the top surface of the topmost paper P1
of the paper P in the paper feed tray 6, which decreases in number by
feeding, and the bottom surface of the suction belt 2 within a certain
range. Based on a detection signal of the sheet top sensor 3, by
controlling an elevating mechanism not depicted which moves a bottom
plate 61 of the paper feed tray 6 up and down to adjust the height of the
bottom plate 61, the feeding device 200 causes the distance h between the
top surface of the topmost paper P1 of the paper P placed on the bottom
plate 61 and the bottom surface of the suction belt 2 to be within the
certain range.

[0011] On the downstream side in the conveying direction from the suction
belt 2, a pair of carriage rollers 8 is disposed and the pair of carriage
rollers 8 further conveys the paper P conveyed by the suction belt 2
reaching between the two rollers towards the downstream side.
Furthermore, on the downstream side in the conveying direction from the
pair of carriage rollers 8, a feed sensor 9 that detects the passing of
the paper P is provided.

[0012] The feeding operation of the feeding device 200 illustrated in FIG.
16 will be explained.

[0013] When a command to start feeding is received from a control unit of
an image forming apparatus body not depicted, as illustrated in FIG. 17,
the blowing of the blowing device 1 and the suction of the suction device
40 are started while the suction belt 2 is being stopped. As the blowing
device 1 is started to blow air, the air is blown to the leading edge
portion of the paper P as indicated by the arrow A in FIG. 17 and the
topmost paper P1 of the stacked paper P is lifted. By starting the
suction of the suction device 40, a negative pressure is generated as
indicated by the arrow B in FIG. 17 and the topmost paper P1 lifted is
attracted on the suction belt 2.

[0014] After an elapse of a given time (for example, 3 seconds) from the
start of the blowing by the blowing device 1 and the suction by the
suction device 40, while the blowing device 1 and the suction device 40
are in operation, as indicated in FIG. 18, the drive of the suction belt
2 and the pair of carriage rollers 8 is started. The suction belt 2
receives the drive transmitted and starts the surface movement in the
arrow C direction indicated in FIG. 18, resulting in the topmost paper P1
attracted on the bottom surface of the suction belt 2 being conveyed
towards the downstream side in the conveying direction and reaching the
pair of carriage rollers 8. The rotation of the pair of carriage rollers
8 in the arrow G direction indicated in FIG. 18 conveys the topmost paper
P1 further towards the downstream side.

[0015] As depicted in FIG. 19, when the leading edge of the topmost paper
P1 conveyed by the suction belt 2 and the pair of carriage rollers 8 is
detected by the feed sensor 9, the drive of the suction belt 2 is
stopped. When the drive of the suction belt 2 is stopped while the
suction device 40 is in operation, a force to stop conveying acts on a
portion of the paper P1, at which the paper P1 is attracted on the
suction belt 2. However, in the feeding device 200, the respective
members are arranged such that a conveying force given to the paper P1 by
the pair of carriage rollers 8 is substantially greater than the force to
stop conveying. Therefore, the topmost paper P1 is continued to be
conveyed by the pair of carriage rollers 8 while the suction belt 2 is
being stopped.

[0016] The sheet that subsequently comes to the top of the paper P after
the topmost paper P1 is defined as a next topmost paper P2. As indicated
in FIGS. 17 to 19, while the topmost paper P1 is attracted on the suction
belt 2, the leading edge portion of the next topmost paper P2 flaps below
the topmost paper P1 as it is receiving the blowing air from the blowing
device 1. Accordingly, the leading edge portion side of the next topmost
paper P2 is being separated from the paper P below.

[0017] Then, immediately after the trailing edge portion of the topmost
paper P1 passes through the suction area of the suction device 40, as
depicted in FIG. 20, by the flow of air formed between the blowing device
1 and the suction device 40, the next topmost paper P2 is lifted and
attracted on the suction belt 2.

[0018] According to a predetermined feeding interval, after an elapse of a
given time from the operational timing of the feed sensor 9 detecting the
leading edge of the topmost paper P1 as indicated in FIG. 19, the drive
of the suction belt 2 is resumed. Consequently, similarly to the topmost
paper P1 depicted in FIG. 18, the next topmost paper P2 is conveyed by
the suction belt 2 towards the downstream side in the conveying direction
reaching the pair of carriage rollers 8, and is further conveyed towards
the downstream side by the pair of carriage rollers 8.

[0019] While the blowing device 1, the suction device 40, and the pair of
carriage rollers 8 are in operation, the drive of the suction belt 2 is
controlled on and off. The operations depicted in FIGS. 18 to 20 are
repeated, thereby sequentially feeding the paper P one by one towards the
image forming section.

[0020] The feeding device that separates and feeds the sheet by using the
flow of air can feed the sheets faster than the feeding device that
separates and feeds the sheet by the frictional separation method. The
reasons for this are as follows. In the frictional separation method,
because it requires a time to frictionally separate the sheet, it has
certain limitations with respect to high linear speed and high
productivity. On the other hand, in the feeding device illustrated with
reference to FIGS. 16 to 20, right after the previous sheet attracted on
the suction belt passes through the suction area, the next sheet is
separated from the further next sheet and attracted on the suction belt.
Consequently, because it only needs to convey the sheet that is separated
by the flow of air, it can deal with the high linear speed and high
productivity.

[0021] The feeding device that separates and feeds the sheet using the
flow of air has an advantage of feeding the sheet fast. This leads to the
fact that a large number of sheets are consumed in a short period of
time. Accordingly, with a single use of such feeding device, a user may
have to replenish the sheets to the sheet housing unit in the feeding
device very often.

[0022] As a structure to reduce replenishing frequency of the sheets, a
feeding structure having feeding devices connected in series can be
exemplified. As the structure to connect the feeding devices, Japanese
Patent Application Laid-open No. 2009-57155 discloses a structure of
connecting the feeding devices of the frictional separation type. In the
feeding devices disclosed therein, one feeding device is arranged between
an image forming apparatus body and the other feeding device and is
structured to pass the sheet fed from the other feeding device through
inside of the one feeding device. In the structure disclosed therein, a
dedicated feed path is provided for the sheet fed from the other feeding
device bypassing a sheet conveying unit that separates and feeds the
sheet in the sheet housing unit of the one feeding device disposed on the
image forming apparatus body side.

[0023] FIG. 21 is a diagram illustrating an example of an exemplary image
forming apparatus with a feeding device disposed on the image forming
apparatus side that is combined with a structure provided with a
dedicated feed path for the sheet fed from other feeding device and a
feeding device that separates and feeds the sheet using the flow of air.

[0024] An image forming apparatus 10 depicted in FIG. 21 is structured
with a first feeding device 200a and a second feeding device 200b
connected together with an image forming apparatus 10a. In the image
forming apparatus 10, a dedicated external device sheet feed path 13 is
provided so as to bypass the suction belt 2 forming the sheet conveying
unit that separates and feeds the sheet from the paper feed tray 6 in the
first feeding device 200a.

[0025] Consequently, with the structure connecting the feeding devices
together, it requires a feed path dedicated for the sheet fed from the
feeding device on the upstream side towards the image forming apparatus
body to be provided in the feeding device on the downstream side.
Providing the dedicated feed path causes an increase in component cost
and an increase in space for the dedicated feed path for the feeding
device on the downstream side.

SUMMARY OF THE INVENTION

[0026] It is an object of the present invention to at least partially
solve the problems in the conventional technology.

[0027] According to an aspect of the present invention, there is provided
a feeding device including: a sheet housing unit in which a plurality of
sheets, nearly horizontal, is stacked; a sheet conveying unit that
includes an endless belt member, which faces a top surface of a topmost
sheet positioned at top of the sheets stacked in the sheet housing unit
and is disposed to have a gap from the top surface of the topmost sheet
when feeding of the sheets stacked in the sheet housing unit is not
performed, and a suction unit disposed inside the belt member, the sheet
conveying unit attracting the topmost sheet on an outer surface of the
belt member by generating a negative pressure in the suction unit and
conveying the attracted topmost sheet towards a subsequent step by
endlessly moving the belt member; and a sheet lifting unit that lifts the
topmost sheet to a position where the topmost sheet is attracted on the
surface of the belt member by the negative pressure generated by the
suction unit, wherein the feeding device is configured to be connected to
another feeding device that houses sheets and to feed the sheet fed from
the other feeding device to the subsequent step, the feeding device
further comprises an external device sheet conveying unit that conveys
the sheet fed from the other feeding device to the gap between the
topmost sheet in the sheet housing unit and the belt member, and in
feeding the sheet fed from the other feeding device to the subsequent
step, the sheet lifting unit is stopped while the suction unit, the belt
member, and the external device sheet conveying unit are operated.

[0028] According to another aspect of the present invention, there is
provided an image forming apparatus including: an image forming section
that forms an image on a sheet of a recording medium; and a paper feeding
unit that feeds the sheet to the image forming section and includes: a
sheet housing unit in which the plurality of sheets, nearly horizontal,
is stacked; a sheet conveying unit that includes an endless belt member,
which faces a top surface of a topmost sheet positioned at top of the
sheets stacked in the sheet housing unit and is disposed to have a gap
from the top surface of the topmost sheet when feeding of the sheets
stacked in the sheet housing unit is not performed, and a suction unit
disposed inside the belt member, the sheet conveying unit attracting the
topmost sheet on an outer surface of the belt member by generating a
negative pressure in the suction unit and conveying the attracted topmost
sheet towards a subsequent step by endlessly moving the belt member; and
a sheet lifting unit that lifts the topmost sheet to a position where the
topmost sheet is attracted on the surface of the belt member by the
negative pressure generated by the suction unit, wherein the feeding
device is configured to be connected to another feeding device that
houses sheets and to feed the sheet fed from the other feeding device to
the subsequent step, the feeding device further comprises an external
device sheet conveying unit that conveys the sheet fed from the other
feeding device to the gap between the topmost sheet in the sheet housing
unit and the belt member, and in feeding the sheet fed from the other
feeding device to the subsequent step, the sheet lifting unit is stopped
while the suction unit, the belt member, and the external device sheet
conveying unit are operated.

[0029] The above and other objects, features, advantages and technical and
industrial significance of this invention will be better understood by
reading the following detailed description of presently preferred
embodiments of the invention, when considered in connection with the
accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a diagram explaining an image forming apparatus according
to an embodiment of the present invention;

[0031] FIG. 2 is a diagram explaining a copying machine that is the image
forming apparatus body according to the embodiment;

[0032] FIG. 3 is a diagram explaining an overview of a feeding device
illustrating the vicinity of a paper feed tray;

[0033] FIG. 4 is a perspective view illustrating the vicinity of the paper
feed tray depicted in FIG. 3;

[0034] FIG. 5 is a perspective view illustrating the vicinity of the paper
feed tray with a paper feed unit removed from the state depicted in FIG.
4;

[0035] FIG. 6 is a perspective view of the paper feed unit viewed from
below;

[0036] FIG. 7 is an enlarged perspective view of the paper feed unit near
the rear end in a sheet height non-detecting state;

[0037] FIG. 8 is an enlarged perspective view of the paper feed unit near
the rear end in a sheet height detecting state;

[0038] FIG. 9 is a schematic diagram of a sheet top sensor;

[0039] FIG. 10 is a diagram explaining the height of a top surface of a
topmost sheet being in a normal state;

[0040] FIG. 11 is a diagram explaining the height of the top surface of
the topmost sheet being below the normal position;

[0041] FIG. 12 is a diagram explaining a bottom plate being elevated from
the state depicted in FIG. 11;

[0042] FIG. 13 is a diagram explaining the feeding device at the
operational timing of the topmost sheet being lifted;

[0043] FIG. 14 is a diagram of the feeding device explaining the detection
of sheet height;

[0044] FIG. 15 is a diagram explaining a sheet on the upstream side
passing the feeding device;

[0045] FIG. 16 is a diagram explaining an example of the feeding device
that separates and feeds sheets using the flow of air;

[0046] FIG. 17 is a diagram explaining the state of starting the blowing
of a blowing device and the suction of a suction device of the feeding
device depicted in FIG. 16;

[0047] FIG. 18 is a diagram explaining the state of starting the drive of
a suction belt and a pair of carriage rollers from the state depicted in
FIG. 17;

[0048] FIG. 19 is a diagram explaining the state of stopping the drive of
the suction belt from the state depicted in FIG. 18;

[0049] FIG. 20 is a diagram explaining the state of the trailing edge of
the sheet passing the suction area from the state depicted in FIG. 19;
and

[0050] FIG. 21 is a diagram explaining an image forming apparatus having a
feeding device provided with a dedicated feed path for the sheet fed from
other feeding device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] An exemplary embodiment of a feeding device to which the present
invention is applied will be described below. The overall structure and
operation of an image forming apparatus body connectable with the feeding
device according to an embodiment of the present invention will be
explained.

[0052] FIG. 2 is a schematic diagram illustrating the structure of a
copying machine 100 that is the image forming apparatus body according to
the present embodiment.

[0053] The copying machine 100 has functions as a so-called digital color
copying machine that reads an original by scanning, digitalizes the
original thus read, and duplicates the original onto a sheet.

[0054] As depicted in FIG. 2, the copying machine 100 is provided with
components such as an image forming section 101, a scanning unit 102, a
fixing unit 103, and a discharging unit 104. On the lower portion of the
copying machine 100, a multi-stage paper feeding unit 105 is provided. In
stages of the paper feeding unit 105, main body paper feed trays 106,
each of which is stacked with a recording medium in sheet such as plain
paper, coated paper including coat paper, and an OHP transparency sheet
(hereinafter, referred to as sheet) are arranged, respectively. In each
of the main body paper feed trays 106, a main body tray bottom plate 125,
a pick-up roller 108, a feed roller 109, a reverse roller 110, and a
paper feeding roller 126 are disposed. The main body tray bottom plate
125 is structured to move up and down in the vertical direction depending
on the remaining number of sheets stacked inside the main body paper feed
tray 106. The pick-up roller 108 gives the sheet at the top of the sheets
placed a force to go forward and conveys the sheet towards a pair of
rollers composed of the feed roller 109 and the reverse roller 110. The
feed roller 109 and the reverse roller 110 form a separating unit that
conveys only a single sheet at the top towards the paper feeding roller
126 when a plurality of sheets is conveyed by the pick-up roller 108.

[0055] More specifically, a single sheet at the top in the main body paper
feed tray 106 is supplied by the rotation of the pick-up roller 108 and
is separated one by one by the reverse roller 110.

[0056] The separated sheet is sent out from the main body paper feed tray
106 by the rotation of the feed roller 109 and the paper feeding roller
126 and is conveyed to a pair of registration rollers 111 in the image
forming section 101 disposed on the downstream side in the sheet
conveying direction. The sheet thus separated and conveyed is temporarily
held to wait by abutting on a nip of the pair of registration rollers
111. The sheet is then sent to a secondary transfer nip for image
forming.

[0057] The scanning unit 102 is provided with an exposure glass 131 the
upper surface of which is brought into contact with a scanning surface of
the original, and a lens 134 and a CCD camera 135 for reading an original
image as image information. The scanning unit 102 is also provided with a
first traveling body 132 that has a light source and a reflective mirror
and moves corresponding to a document read position, and a second
traveling body 133 that moves in response to the movement of the first
traveling body 132 so that the distance of an optical path from the
reflective mirror in the first traveling body 132 to the CCD camera 135
remains constant. On the upper portion of the scanning unit 102, an
automatic document feeder 136 is disposed.

[0058] In the substantially central portion of the image forming section
101, an intermediate transfer belt 121 is disposed and, on the upper
portion of the intermediate transfer belt 121, four units of image
forming units 122 which form toner images in respective colors on
photosensitive elements 138 corresponding to the respective colors are
disposed. In the periphery of the photosensitive element 138 of each
image forming unit 122, a charging unit 139 that uniformly charges the
surface of the photosensitive element 138, a developing unit 140 that
develops a latent image formed on the surface of the photosensitive
element 138 as a toner image, a photosensitive element cleaning device
141 that removes the toner image remaining on the surface of the
photosensitive element 138 after the toner image is transferred onto the
intermediate transfer belt 121, and the like are disposed. Above the four
image forming units 122, an exposing unit 123 that irradiates the
photosensitive elements of the image forming units 122 of respective
colors with exposure lights corresponding to the respective colors to
form the latent images on the photosensitive elements is disposed.

[0059] Below the intermediate transfer belt 121, a secondary transfer
roller 137 that forms the secondary transfer nip with the intermediate
transfer belt 121 therebetween is disposed. On the downstream side in a
moving direction of the surface of the intermediate transfer belt 121
from the secondary transfer nip, an intermediate transfer belt cleaning
device 130 that removes residual toner remaining on the surface of the
intermediate transfer belt 121 after passing through the secondary
transfer nip is disposed.

[0060] Further below the fixing unit 103 disposed below the intermediate
transfer belt 121, a duplex device 124 that conveys the sheet having an
image formed on its front surface by the fixing unit 103 towards the
transfer position with its rear surface facing up is disposed. On the
left side of the fixing unit 103 in FIG. 2, discharging rollers 127 that
discharge the sheet having an image formed on its front surface by the
fixing unit 103 towards the discharging unit 104 are disposed. Further
below the discharging rollers 127, reverse discharging rollers 128 that
discharge the sheet to the discharging unit 104 such that the front
surface of the sheet having an image formed faces downward are disposed.
Between the fixing unit 103 and the discharging rollers 127, a
bifurcating claw 129 that switches a feed path of the sheet passing
through the fixing unit 103 to a feed path heading towards the
discharging rollers 127 or a feed path heading towards the reverse
discharging rollers 128 or the duplex device 124 is disposed.

[0061] The copying machine 100 according to the present embodiment is
provided with a feeding device 200 as a separate paper feeding unit from
the paper feeding unit 105, and a bypass tray 300 above the feeding
device 200. When image forming is performed, sheets are sequentially
supplied being separated one by one from the main body paper feed tray
106 selected in the paper feeding unit 105, the bypass tray 300, or the
feeding device 200.

[0062] The feeding device 200 according to the present embodiment will be
described.

[0063] FIG. 1 is a diagram explaining an image forming apparatus 10
connected with two units of the feeding devices 200 (200a and 200b) that
sequentially supplies the sheets to the copying machine 100.

[0064] As depicted in FIG. 1, each of the two feeding devices 200 is
provided with an upper paper feed tray 6 (6a or 6c) and a lower paper
feed tray 6 (6b or 6d). Above each of the four paper feed trays 6, a
suction belt 2 and a suction device 40 that separate and feed paper P
stacked in the paper feed tray 6 are disposed. Each of the two feeding
devices 200 is structured with a pair of exit rollers 80 (80a or 80b)
provided at the downstream end portion of the feed path in the feeding
device to feed the paper P to the subsequent step.

[0065] FIG. 3 is a schematic diagram illustrating the vicinity of the
first lower paper feed tray 6b disposed in the lower portion of the first
feeding device 200a out of the four paper feed trays 6. FIG. 4 is a
perspective view illustrating the vicinity of the first lower paper feed
tray 6b depicted in FIG. 3. In FIG. 4, illustration of a pair of upstream
side paper carriage rollers 210 is omitted. The structure of the vicinity
of the second lower paper feed tray 6d disposed in the lower portion of
the second feeding device 200b out of the other three paper feed trays 6
is the same as that depicted in FIG. 3. The other two paper feed trays 6,
i.e., the first upper paper feed tray 6a and the second upper paper feed
tray 6c disposed at the upper portion of each feeding device 200 only
differ in terms of the pair of upstream side paper carriage rollers 210
not being provided, and other structure is the same as that depicted in
FIG. 3.

[0066] As depicted in FIGS. 3 and 4, the feeding device 200 is provided
with the paper feed tray 6 that is a sheet housing unit provided with a
bottom plate 61 where a bundle of the paper P that is a plurality of
sheets is stacked. Above the paper feed tray 6, a paper feed unit 22
provided with the suction belt 2 and the suction device 40 is disposed.
The suction belt 2 has suction holes opened penetrating from the front
surface through the rear surface of the belt over the entire belt in its
circumferential direction. When the suction device 40 generates a
negative pressure below, it acts on the paper P to be attracted on the
bottom surface of the suction belt 2. The paper feed unit 22 thus
structured forms a sheet conveying unit that picks up the paper P one by
one at the top of the bundle of the paper P placed in the paper feed tray
6 and feeds sheets to the copying machine 100 that is the image forming
apparatus body.

[0067] As depicted in FIG. 4, in the paper feed tray 6, side fences 23
that guide side surfaces of the bundle of the paper P stacked on the
bottom plate 61 in its width direction (direction orthogonal to the
feeding direction) are provided on both sides and an end fence 24 that
holds the trailing edge portion at the back of the bundle of the paper P
in the feeding direction is provided.

[0068] On the side fence 23, a side air outlet 71 that is an outlet for
the air from a blowing unit used for lifting and separating the paper P
is provided. The feeding device 200 of the present embodiment is
center-referenced so that both of the two side fences 23 are moved
according to the paper size. Consequently, regardless of the paper size,
the air blown out from a center air outlet 11 can be blown towards the
center of the paper P.

[0069] The feeding device 200 is provided with a sheet top sensor 3 on the
upstream side in the sheet conveying direction (direction going from
right to left in FIG. 3) from the suction belt 2. In the feeding device
200, it is necessary to maintain a distance h between the top surface of
the topmost paper P1 of the paper P in the paper feed tray 6 that
decreases in number by feeding and the bottom surface of the suction belt
2 within a certain range. Accordingly, the height of the top surface of
the topmost paper P1 is detected by the sheet top sensor 3 and, based on
a detecting signal of the sheet top sensor 3, the drive of a bottom plate
elevating motor M1 that is a driving source of an elevating mechanism not
depicted that moves the bottom plate 61 of the paper feed tray 6 up and
down is controlled. Consequently, the height of the bottom plate 61 is
adjusted and controlled such that the distance h between the top surface
of the topmost paper P1 of the paper P placed on the bottom plate 61 and
the bottom surface of the suction belt 2 is within the certain range. In
the feeding device 200 of the present embodiment, the sheet top sensor 3
is mounted on a frame of the paper feed unit 22.

[0070] FIG. 5 is a perspective view illustrating the vicinity of the paper
feed tray 6 with the paper feed unit 22 being removed from the state
depicted in FIG. 4.

[0071] As depicted in FIG. 5, above a paper hold-back member 7 arranged
directly under the paper feed unit 22, a blowing device 1 that lifts and
separates sheets by blowing air from the center air outlet 11 is
disposed.

[0072] In the feeding device 200, the blowing device 1 such as a blower
blows air towards the leading edge portion and side edge portions of the
sheets of the paper P stacked in the paper feed tray 6. By the blowing of
air, the air is sent between the sheets of the paper P to lift the
topmost paper P1 to the height of the suction belt 2 and to have the
topmost paper P1 attracted on the suction belt 2 by the negative pressure
the suction device 40 generates.

[0073] While the topmost paper P1 is attracted on the suction belt 2, a
belt driving motor 26 is driven to move the suction belt 2 in endless
movement in the clockwise direction indicated in FIG. 3 to make the
suction belt convey the topmost paper P1 to the copying machine 100 and
then, image forming is performed.

[0074] The blowing device 1 not only lifts the topmost paper P1 to a given
height by pumping air between the sheets of the paper P, but also
separates the sheets by blowing air to the area in a direction of the
given height.

[0075] Between the blowing device 1 and the paper P, the paper hold-back
member 7 is disposed to hold back the leading edge portion of the bundle
of the paper P preventing sheets other than the topmost paper P1 from
being conveyed. The sheet top sensor 3 that detects the height of the top
surface of the topmost paper P1 by abutting on the topmost surface of the
bundle of the paper P is provided to maintain the distance h between the
position of the top surface of the bundle of the paper P that decreases
in number by feeding the paper P and the suction belt 2 to be constant.
The sheet top sensor 3 has an actuator 4 and a photo sensor 5 that
detects the position of the actuator 4.

[0076] In the feeding device 200, the actuator 4 swings by the reduction
of the paper P in number and the photo sensor 5 detects changes of the
position by the swing. Based on this detection signal, the drive of the
bottom plate elevating motor M1 is controlled to raise the bottom plate
61 by the elevating mechanism not depicted so as to control the distance
h between the top surface of the topmost paper P1 of the paper P placed
on the bottom plate 61 and the bottom surface of the suction belt 2 to be
within a constant range.

[0077] The bundle of the paper P is aligned with the surface of the
leading edge as a reference surface to fit the paper size in the paper
feed tray 6.

[0078] On the downstream side in the conveying direction from the suction
belt 2, a pair of carriage rollers 8 is disposed to further convey the
paper P, which has been conveyed by the suction belt 2 and reached
between the two rollers, towards the downstream side. The force to go
forward of the pair of carriage rollers 8 is arranged to be greater than
that of the suction belt 2. On the downstream side in the conveying
direction from the pair of carriage rollers 8, a feed sensor 9 that
detects the passing of the paper P is provided.

[0079] The feeding operation performed by the feeding device 200
illustrated in FIG. 3 will be explained.

[0080] When a command to start feeding is received from a control unit of
the copying machine 100, while the suction belt 2 is being stopped, the
blowing of the blowing device 1 and the suction of the suction device 40
are started. When the blowing device 1 is started to blow air, the air is
blown to the leading edge portion of the paper P and the topmost paper P1
of the stacked paper P is lifted. When the suction device 40 starts
sucking, a negative pressure is generated below the suction device 40 and
the topmost paper P1 lifted is attracted on the suction belt 2.

[0081] After an elapse of a given time (for example, 3 seconds) from the
start of the blowing of the blowing device 1 and the suction of the
suction device 40, while the blowing device 1 and the suction device 40
are in operation, the drive of the suction belt 2 and the pair of
carriage rollers 8 is started. The suction belt 2 receives the drive
transmitted and starts the surface movement of the suction belt 2 in the
clockwise direction indicated in FIG. 3. This results in the topmost
paper P1 attracted on the bottom surface of the suction belt 2 being
conveyed towards the downstream side in the conveying direction and
reaching the pair of carriage rollers 8. The topmost paper P1 is then
further conveyed to the downstream side by the pair of carriage rollers
8.

[0082] When the leading edge of the topmost paper P1 conveyed by the
suction belt 2 and the pair of carriage rollers 8 is detected by the feed
sensor 9, the drive of the suction belt 2 is stopped.

[0083] The reason to control the drive of the suction belt 2 to be stopped
in this way is as follows. That is, if the suction belt 2 is driven
continuously, at the time of the topmost paper P1 starts passing through
the suction area of the suction device 40 as the topmost paper P1 is
conveyed, a next topmost paper P2 that is the subsequent paper P below
the topmost paper P1 is also attracted on the suction belt 2. If the
suction belt 2 is driven at this time, the next topmost paper P2 may be
conveyed together with the topmost paper P1 resulting in so-called double
feed.

[0084] Accordingly, when the leading edge of the topmost paper P1 is
detected by the feed sensor 9, the drive of the suction belt 2 is
stopped. The topmost paper P1 at this point is sandwiched between the two
rollers of the pair of carriage rollers 8. Because the pair of carriage
rollers 8 is continued to be driven even after the drive of the suction
belt 2 is stopped, the topmost paper P1 is continued to be conveyed. In
this case, if the force to go forward by the pair of carriage rollers 8
is smaller than that of the suction belt 2, the topmost paper P1 is held
stuck on the suction belt 2 and the conveyance of the topmost paper P1 is
stopped. Accordingly, as described above, the force to go forward given
by the pair of carriage rollers 8 is arranged to be greater than that of
the suction belt 2.

[0085] By continuing to drive the pair of carriage rollers 8 even after
the drive of the suction belt 2 is stopped, the conveyance of the topmost
paper P1 is continued.

[0086] While the topmost paper P1 is attracted on the suction belt 2, the
leading edge portion of the next topmost paper P2 flaps below the topmost
paper P1 as it receives the blowing air from the blowing device 1.
Accordingly, the leading edge portion of the next topmost paper P2 is
being separated from the paper P below.

[0087] Then, immediately after the trailing edge portion of the topmost
paper P1 passes through the suction area of the suction device 40, by the
flow of the air formed between the blowing device 1 and the suction
device 40, the next topmost paper P2 is lifted and attracted on the
suction belt 2.

[0088] According to the predetermined feeding interval, the drive of the
suction belt 2 is then resumed after an elapse of a given time from the
operational timing of the feed sensor 9 detecting the leading edge of the
topmost paper P1. Consequently, similarly to the topmost paper P1, the
next topmost paper P2 is conveyed by the suction belt 2 towards the
downstream side in the conveying direction to reach the pair of carriage
rollers 8, and is further conveyed towards the downstream side by the
pair of carriage rollers 8.

[0089] While the blowing device 1, the suction device 40, and the pair of
carriage rollers 8 are in operation, repeating the controls of setting
off the drive of the suction belt 2 when the feed sensor 9 detects the
leading edge of the paper P and setting on the drive of the suction belt
2 after an elapse of the given time from the operational timing of the
feed sensor 9 detecting the leading edge of the paper P makes the paper P
in the paper feed tray 6 to be sequentially fed one by one towards the
copying machine 100.

[0090] FIG. 6 is a perspective view of the paper feed unit 22 viewed from
below.

[0091] The paper feed unit 22 is provided with the suction belt 2 with
suction holes opened in the entire circumferential area and the belt
driving motor 26 connected to the suction belt 2. By driving the belt
driving motor 26 at predetermined operational timing, the suction belt 2
can be rotary driven.

[0092] Inside the suction belt 2, a suction chamber 41 is provided. The
suction chamber 41 is connected to a suction blower 28 via a suction duct
27 and is structured to maintain an appropriate static suction pressure
at an opening portion not depicted of the suction chamber 41.
Accordingly, in the feeding device 200, the suction chamber 41, the
suction duct 27, and the suction blower 28 form the suction device 40. By
driving the suction blower 28, the suction is performed through the
suction holes of the suction belt 2 at the position facing the opening
portion of the suction chamber 41 not depicted.

[0093] FIGS. 7 and 8 are enlarged perspective views of the paper feed unit
22 near the rear end portion in the sheet conveying direction with a unit
rear end plate 221 at the rear end of the paper feed unit 22 being
removed. FIG. 7 is the enlarged perspective view when the height of the
top surface of the topmost paper P1 is not detected by the sheet top
sensor 3, and FIG. 8 is the enlarged perspective view when the height of
the top surface of the topmost paper P1 is detected by the sheet top
sensor 3.

[0094] The actuator 4 of the sheet top sensor 3 is pivotally mounted via a
support shaft 31 to the frame of the paper feed unit 22. On one end of
the actuator 4, a filler 36 that is actually brought into contact with
the sheets and detects the height of the sheets is provided and, on the
other end of the actuator 4 opposite to the filler 36 across the support
shaft 31, a position detecting portion 32 the position of which is
detected by the photo sensor 5 is provided.

[0095] With reference to FIGS. 9 to 12, the detection of the height of the
top surface of the topmost paper P1 by the sheet top sensor 3 and the
control of the height of the top surface of the topmost paper P1
performed based on the detection will be explained.

[0096] FIG. 9 is a schematic diagram of the sheet top sensor 3. As
indicated by the arrow E in FIG. 9, the actuator 4 is rotatable about the
support shaft 31.

[0097] FIG. 10 is a diagram explaining the height of the top surface of
the topmost paper P1 of the paper P stacked in the paper feed tray 6
being in a normal state. In this case, the position detecting portion of
the actuator 4 is positioned at the detecting position of the photo
sensor 5, and thus the photo sensor 5 is in a detecting state.

[0098] When the number of paper P is decreased by feeding from the
condition illustrated in FIG. 10, as depicted in FIG. 11, the height of
the top surface of the topmost paper P1 is lowered and the actuator 4
rotates in the arrow E1 direction indicated in FIG. 11. Under this
condition, the position detecting portion of the actuator 4 is not
positioned at the detecting position of the photo sensor 5, and thus the
photo sensor 5 is in a non-detecting state.

[0099] As depicted in FIG. 11, when the photo sensor 5 is in the
non-detecting state, the bottom plate elevating motor M1 is driven to
operate the elevating mechanism not depicted to raise the bottom plate 61
as indicated by the arrow F in FIG. 12.

[0100] When the bottom plate 61 is raised from the condition depicted in
FIG. 11, as depicted in FIG. 12, the height of the top surface of the
topmost paper P1 is raised and thus, the actuator 4 rotates in the arrow
E2 direction indicated in FIG. 12. Accordingly, the position detecting
portion of the actuator 4 comes to the detecting position of the photo
sensor 5, and thus the photo sensor 5 becomes the detecting state again.
As depicted in FIG. 12, when the photo sensor 5 becomes the detecting
state, the drive of the bottom plate elevating motor M1 is halted to stop
raising the bottom plate 61 by the elevating mechanism.

[0101] With the sheet top sensor 3 thus structured, the photo sensor 5 can
detect the position of the actuator 4 and thus, the position of the
topmost surface of the bundle of the paper P can be detected by the
actuator 4 and the photo sensor 5. To keep the feeding position of the
paper P constant without varying even when the number of paper P
remaining becomes small, the drive of the bottom plate elevating motor M1
is controlled to move the bottom plate 61 up and down based on the
detecting result of the sheet top sensor 3, whereby the feeding position
of the paper P is controlled.

[0102] Further, the feeding device 200 is provided with a position
switching mechanism that switches the position of the actuator 4 of the
sheet top sensor 3 to up and down positions. In the present embodiment,
an actuator spring 33, a pressure arm 35, and a pressure motor 34 form
the position switching mechanism. One end of the actuator spring 33 is
fixed to the frame of the paper feed unit 22 and the other end is fixed
to the end portion of the actuator 4 on the position detecting portion 32
side.

[0103] FIG. 7 depicts the actuator 4 in the up position, and FIG. 8
depicts the actuator 4 in the down position. The detection of the height
of the top surface of the topmost paper P1 by the sheet top sensor 3 is
performed only when the actuator 4 is set in the down position, and not
detected in the up position.

[0104] While the pressure motor 34 is stopped, as depicted in FIG. 8, the
actuator spring 33 acts on the end portion of the actuator 4 on the
position detecting portion 32 side to pull up. By this action, the
opposite end portion of the actuator 4 across the support shaft 31 is
lowered and the filler 36 is brought into contact with the top surface of
the topmost paper P1. In other words, stopping the pressure motor 34 to
set the actuator 4 in the down position turns the detection of the height
of the top surface of the topmost paper P1 by the sheet top sensor 3 to
an on-state.

[0105] On the other hand, when the pressure motor 34 is driven, as
depicted in FIG. 7, the pressure arm 35 is lowered and then is brought
into contact with the end portion of the actuator 4 on the position
detecting portion 32 side and presses the end portion down. By this
downward pressing, the opposite end portion of the actuator 4 across the
support shaft 31 is raised and the filler 36 is separated from the top
surface of the topmost paper P1. In other words, driving the pressure
motor 34 to set the actuator 4 in the up position turns the detection of
the height of the top surface of the topmost paper P1 by the sheet top
sensor 3 to an off-state.

[0106] The drive of the pressure motor 34 that switches the detection by
the sheet top sensor 3 on and off is controlled by a control unit not
depicted provided on the feeding device 200.

[0107] FIG. 13 is a diagram of the feeding device 200 of the present
embodiment explaining the operational timing of the topmost paper P1
being lifted, and FIG. 14 is a diagram explaining the operational timing
of the leading edge of the topmost paper P1 passing the pair of carriage
rollers 8.

[0108] By providing the position switching mechanism that switches the up
and down positions of the actuator 4 of the sheet top sensor 3, as
depicted in FIG. 13, when lifting a sheet, the position of the actuator 4
is set to the up (sheet height non-detecting state) position so that
there is no adverse impact in lifting the sheet.

[0109] As depicted in FIG. 14, when the topmost paper P1 is attracted on
the suction belt 2 and reaches the pair of carriage rollers 8, the
position of the actuator 4 is set to the down (sheet height detecting
state) position. Consequently, the height of the top surface of the next
topmost paper P2 can be detected without having an adverse effect on the
feeding of the topmost paper P1, thereby allowing the distance h aimed to
be maintained.

[0110] Accordingly, the actuator 4 of the feeding device 200 of the
present embodiment moves up and down to repeat contacting with and
separating from the topmost surface of the paper P each time a single
sheet of paper P in the paper feed tray 6 is fed. This makes it possible
to detect the topmost surface of the paper P for maintaining the feeding
position of the paper P constant without imparting any impact in lifting
the sheet.

[0111] In the conventional feeding device 200 explained with reference to
FIGS. 16 to 20, it is structured that, by mounting the sheet top sensor 3
provided with the actuator 4 on the end fence 24, the mounting position
of the actuator 4 is changed according to the difference in position near
the rear end of the paper P for sheet size. In the conventional feeding
device 200, by mounting the sheet top sensor 3 on the end fence 24, the
mounting position of the actuator 4 can be set near the trailing edge of
sheets where blowing by the blowing device 1 is not likely to be
affected.

[0112] The features of the feeding device 200 according to the present
embodiment will be described.

[0113] The first feeding device 200a according to the present embodiment
is connected to the second feeding device 200b that is another feeding
device housing the paper P, and is structured to be able to feed the
paper P fed from the second feeding device 200b to the copying machine
100.

[0114] FIG. 15 is a diagram explaining the paper P fed from the paper feed
tray 6 (6c or 6d) of the second feeding device 200b (hereinafter,
referred to as upstream side paper Pb) depicted in FIG. 1 passing above
the first lower paper feed tray 6b of the first feeding device 200a.

[0115] As depicted in FIG. 15, the feeding device 200 is provided with the
pair of upstream side paper carriage rollers 210 that conveys the
upstream side paper Pb fed from the another feeding device 200 disposed
on the upstream side to the gap between the topmost paper P1 placed in
the paper feed tray 6 and the suction belt 2. The pair of upstream side
paper carriage rollers 210 forms an upstream side paper feed path 14 that
is the feed path for the upstream side paper Pb in the feeding device
200.

[0116] When feeding the upstream side paper Pb to the copying machine 100,
the blowing device 1 is stopped, while the driving sources of the suction
device 40, the belt driving motor 26, and the pair of carriage rollers 8,
and the driving source of the pair of upstream side paper carriage
rollers 210 are operated.

[0117] In the feeding device 200, the paper P lifted by the blowing of the
blowing device 1 that is a lifting unit is sucked by a negative pressure
generated by the suction device 40. Accordingly, by stopping the blowing
device 1, the topmost paper P1 is not lifted with only the negative
pressure of the suction device 40 and, in the same manner as when the
feeding of the paper P stacked in the paper feed tray 6 is not performed,
the gap is formed between the top surface of the topmost paper P1 and the
suction belt 2. Operating the pair of upstream side paper carriage
rollers 210 and the suction device 40 causes the upstream side paper Pb
fed from the second feeding device 200b and conveyed by the pair of
upstream side paper carriage rollers 210 to the gap between the top
surface of the topmost paper P1 and the suction belt 2 to be attracted on
the suction belt 2. Further, by operating the belt driving motor 26, the
upstream side paper Pb attracted on the suction belt 2 can be conveyed
towards the copying machine 100 by the endless movement of the suction
belt 2.

[0118] In the feeding device 200 thus structured, the feed path of the
upstream side paper Pb after being attracted on the suction belt 2 is the
same feed path as when the paper P stacked in the first lower paper feed
tray 6b in the first feeding device 200a is fed. More specifically, the
suction belt 2 and the pair of carriage rollers 8 form a part of the feed
path for the upstream side paper Pb, and the upstream side paper Pb
supplied from the paper feed tray 6 (6c or 6d) of the second feeding
device 200b can be fed to the copying machine 100.

[0119] Thus, a dedicated feed path for the sheet fed from the second
feeding device 200b (the dedicated external device sheet feed path 13 of
the feeding device 200 depicted in FIG. 21) is not required.
Consequently, although it is structured to be connectable with a
plurality of feeding devices 200, an increase in the number of components
for providing the dedicated feed path for the paper P fed from the other
feeding devices 200 and an increase in space for the dedicated feed path
can be prevented.

[0120] In the structure connecting the feeding devices of the frictional
separation type as disclosed in Japanese Patent Application Laid-open No.
2009-57155, a conveying member disposed above the paper feed tray such as
a pick-up roller is a conveying member of an abutment type that provides
a force to go forward abutting on the topmost surface of the sheets
placed in the paper feed tray. The conveying member of the abutment type
can provide the force to go forward by the friction because it is indeed
abutted on the topmost surface of the sheet placed in the paper feed tray
with a certain amount of abutting pressure. Therefore, the force to go
forward cannot be provided unless the sheet that is a conveying subject
is sandwiched between the conveying member and other member (second and
subsequent sheets placed on the bottom plate).

[0121] With such a structure, because the space cannot be formed between
the sheets placed in the paper feed tray and the conveying member, the
conveying member disposed above the paper feed tray cannot be used as a
conveying member to convey the sheet supplied from the feeding device
connected on the upstream side.

[0122] In contrast, as the feeding device 200 of the present embodiment,
in the structure that conveys using the suction device 40 and the suction
belt 2, the sheet is conveyed while the sheet is attracted on the suction
belt 2 by the suction. Therefore, the force to go forward can be provided
by the conveying member (suction belt 2) even when no other member is
present below the rear surface of the sheet that is a conveying subject.
Consequently, the suction belt that is a conveying member disposed above
the paper feed tray can be used as the conveying member to convey the
sheet supplied from the feeding device connected on the upstream side.

[0123] In the feeding device 200, the photo sensor 5 and the support shaft
31 are disposed above the upstream side paper feed path 14 and, when
detecting the height of the top surface of the topmost paper P1, the
actuator 4 crosses the upstream side paper feed path 14. However, when
conveying the upstream side paper Pb, as depicted in FIG. 15, the
position of the actuator 4 is set to the up (sheet height non-detecting
state) position so that the conveyance of the upstream side paper Pb is
not obstructed by the actuator 4.

[0124] In the feeding device 200, when conveying the upstream side paper
Pb, the blowing device 1 is stopped so that the conveyance of the
upstream side paper Pb is not obstructed by the paper P in the paper feed
tray 6. As the structure not obstructing the conveyance of the upstream
side paper Pb by the paper P, a structure may be adopted that performs
control to widen the gap between the top surface of the topmost paper P1
and the bottom surface of the suction belt 2 by lowering the bottom plate
61 of the paper feed tray 6, instead of the structure that stops the
blowing device 1.

[0125] The image forming apparatus 10 according to the present embodiment
is provided with the feeding device 200 that can prevent an increase in
the number of components for connection and an increase in space for the
dedicated feed path, whereby an affordable and space saving image forming
apparatus that is connectable to the feeding devices can be provided to
the user.

[0126] The feeding device 200 of the image forming apparatus 10 according
to the present embodiment is a multi-stage feeding device composed of the
upper paper feed trays 6 (6a and 6c) and the lower paper feed trays 6 (6b
and 6d). However, the features of the present embodiment can be applied
to a combination of single stage paper feed trays (a combination of only
the lower paper feed trays 6 (6b and 6d) in FIG. 1).

[0127] As described in the foregoing, the feeding device 200 according to
the present embodiment is provided with the paper feed tray 6, the paper
feed unit 22, and the blowing device 1. The paper feed tray 6 is a sheet
housing unit, the paper feed unit 22 is a sheet conveying unit, and the
blowing device 1 is a sheet lifting unit. In the paper feed tray 6, a
plurality of sheets of the paper P can be placed, which are nearly
horizontal. The paper feed unit 22 is provided with the suction belt 2
that is an endless belt member and the suction device 40 that is a
suction unit disposed inside the suction belt 2. The suction belt 2 is
disposed so as to face the top surface of the topmost paper P1 that is
the topmost sheet positioned at the top of the paper P stacked in the
paper feed tray 6 and to have a gap from the top surface of the topmost
paper P1 when the feeding of the paper P stacked in the paper feed tray 6
is not performed. In the paper feed unit 22, the suction device 40
generates a negative pressure to attract the topmost paper P1 on the
suction belt 2 below its outer surface and the suction belt 2 moves
endlessly. Thus, the topmost paper P1 is attracted on the suction belt 2
to be conveyed towards the copying machine 100 that is in a subsequent
step. The blowing device 1 blows air towards near the leading edge
portion of the topmost paper P1 to lift the topmost paper P1 to the
position where the topmost paper P1 can be attracted on the surface of
the suction belt 2 by the negative pressure generated by the suction
device 40. The first feeding device 200a that is a feeding device is
connectable to the second feeding device 200b that is the other feeding
device housing the upstream side paper Pb of sheets and is capable of
feeding the upstream side paper Pb fed from the second feeding device
200b to the copying machine 100. The feeding device 200 is provided with
the pair of upstream side paper carriage rollers 210 that is an external
device sheet conveying unit conveying the upstream side paper Pb to the
gap between the topmost paper P1 in the paper feed tray 6 and the belt
member. When feeding the upstream side paper Pb to the copying machine
100, the blowing device 1 is stopped while the suction device 40, the
suction belt 2, and the pair of upstream side paper carriage rollers 210
are operated. Stopping the blowing device 1 forms the gap between the top
surface of the topmost paper P1 and the suction belt 2 as in the same
state as when the feeding of the paper P stacked in the paper feed tray 6
is not performed. Meanwhile, operating the pair of upstream side paper
carriage rollers 210 and the suction device 40 allows the upstream side
paper Pb fed from the second feeding device 200b and conveyed by the pair
of upstream side paper carriage rollers 210 to the gap between the top
surface of the topmost paper P1 and the suction belt 2 to be attracted on
the suction belt 2. Further, operating the suction belt 2 enables the
upstream side paper Pb attracted on the suction belt 2 to be conveyed
towards the copying machine 100 that is in the subsequent step by the
endless movement of the suction belt 2.

[0128] In the feeding device 200 thus structured, the feed path of the
upstream side paper Pb after being attracted on the suction belt 2 is the
same as the feed path of when feeding the paper P stacked in the paper
feed tray 6. In other words, the suction belt 2 forms a part of the feed
path of the upstream side paper Pb. As a consequence, it is not necessary
to provide a dedicated feed path for the sheet fed from the second
feeding device 200b, thereby preventing an increase in the number of
components for providing the dedicated feed path and an increase in space
for the dedicated feed path. Because the increase in the number of
components for conveying the upstream side paper Pb and the increase in
space for the dedicated feed path can be prevented, the first feeding
device 200a can be connected to the second feeding device 200b on the
upstream side while preventing the manufacturing cost and device space
from increasing.

[0129] The blowing device 1 that is the lifting unit blows air towards the
leading edge portion of the paper P near the topmost paper P1 of the
paper P stacked in the paper feed tray 6. The blowing device 1 is also an
air discharging unit that blows air to lift the leading edge portions of
the topmost paper P1 and other paper P near the topmost paper P1 and to
separate sheets of the paper P one from the other. With such a structure,
the feeding device 200 separates the paper P by blowing air and sucks the
topmost paper P1 onto the suction belt 2 to separate and convey the paper
P. Because the suction belt 2 is only to convey the paper P in the state
being separated by the blowing of air and suction, compared with the
feeding device of the frictional separation type that frictionally
separates sheets, the feeding device 200 of the present embodiment can
deal with high linear speed and high productivity.

[0130] The feeding device 200 further has the sheet top sensor 3 that is a
sheet top position detecting unit detecting the height of the top surface
of the topmost paper P1 in the paper feed tray 6, and the bottom plate 61
that supports the bottom surface of the paper P stacked in the paper feed
tray 6. Moreover, the feeding device 200 is provided with the elevating
mechanism not depicted that is an elevating unit elevating the bottom
plate 61 in the vertical direction by driving the bottom plate elevating
motor M1 that is a driving source, and an elevation control device not
depicted that is an elevation control unit controlling the operation of
the elevating mechanism by controlling the drive of the bottom plate
elevating motor M1. The elevation control device not depicted controls
the drive of the bottom plate elevating motor M1 based on the detection
result of the sheet top sensor 3 such that the height of the top surface
of the topmost paper P1 of the paper P on the bottom plate 61 comes to a
given height. The sheet top sensor 3 is provided with the actuator 4, the
photo sensor 5 that detects the position of the actuator, and the
position switching mechanism. The actuator 4 is a top surface contacting
member that is brought into contact with the top surface of the topmost
paper P1 and swings up and down to change its position in response to the
changes in the height of the top surface. The photo sensor 5 is a top
surface height detecting sensor that detects the changes in the height of
the top surface of the topmost paper P1 by detecting the changes in the
position of the actuator 4. The position switching mechanism is a
contacting member position control unit that is structured with the
actuator spring 33, the pressure arm 35, and the pressure motor 34 and
can control the position of the actuator 4 regardless of the height of
the top surface of the topmost paper P1. A control unit not depicted
controls the drive of the pressure motor 34 to control the operation of
the position switching mechanism to switch the position of the actuator 4
between the down (sheet height detecting state) position and the up
(sheet height non-detecting state) position.

[0131] The photo sensor 5 is disposed above the upstream side paper feed
path 14 that is an external sheet feed path along which the upstream side
paper Pb conveyed towards the gap between the topmost paper P1 and the
suction belt 2 by the pair of upstream side paper carriage rollers 210
passes. When feeding the upstream side paper Pb to the copying machine
100, the position switching mechanism controls to position the actuator 4
at the up (sheet height non-detecting state) position so that the lower
end portion of the actuator 4 comes above the upstream side paper feed
path 14. Accordingly, the upstream side paper Pb can be conveyed without
being obstructed by the actuator 4.

[0132] The image forming apparatus 10 according to the present embodiment
is provided with the copying machine 100 provided with the image forming
section 101 that forms an image on the paper P as a sheet of a recording
medium, and the feeding device 200 that is a paper feeding unit feeding
the paper P to the copying machine 100. By using the feeding device 200
as the paper feeding unit, an affordable and space saving image forming
apparatus that is connectable to the feeding devices 200 can be provided
to the user.

[0133] In the feeding device according to the present invention, when the
sheet supplied from the other feeding device is fed to the subsequent
step, the elevating unit is being stopped while the suction unit, the
belt member, and the external device sheet conveying unit are in
operation. Stopping the elevating unit results in a gap formed between
the top surface of the topmost sheet and the belt member in the same
manner as when the feeding of the sheets stacked in the sheet housing
unit is not performed. Operating the external device sheet conveying unit
and the suction unit allows the sheet fed from the other feeding device
and conveyed by the external device sheet conveying unit to the gap
between the top surface of the topmost sheet and the belt member to be
attracted on the belt member. Furthermore, operating the belt member
allows the sheet fed from the other feeding device and attracted on the
belt member to be conveyed towards the subsequent step by the endless
movement of the belt member.

[0134] In the feeding device thus structured, the feed path of the sheet
after being attracted on the belt member is the same feed path as when
the sheets stacked in the sheet housing unit are fed. Consequently, a
dedicated feed path for sheets fed from the other feeding device is not
required, whereby an increase in the number of components for providing
the dedicated feed path and an increase in space for the dedicated feed
path can be prevented.

[0135] According to the present invention, an increase in the number of
components for conveying sheets fed from the other feeding device and an
increase in space for the dedicated feed path can be prevented, while the
structure is connectable to the other feeding device on the upstream
side. The present invention thus has a superior effect of preventing
increases in manufacturing cost and in device space.

[0136] Although the invention has been described with respect to specific
embodiments for a complete and clear disclosure, the appended claims are
not to be thus limited but are to be construed as embodying all
modifications and alternative constructions that may occur to one skilled
in the art that fairly fall within the basic teaching herein set forth.